Wafers of silicon for producing photovoltaic cells are cut from the block with the aid of wire saws, the same as in micro-electronics. Previously, this block had been glued together with a glass plate in order to achieve the required support for a complete cut-through. Afterwards, the individual cells only adhere to the gluing seam, because the wire saw also penetrates into the glass block. The sawing process takes place under continuous rinsing with a special medium which mixes with the grains generated during sawing. The wafers solidly adhere to each other in clumps because of this pasty mix, for example, and are very difficult to separate from each other for further processing.
Added to this in a further impeding way is the fact that up to the processing step the wafers need to be kept continuously moist.
Up to now, the wafers were manually cut off in clumps from the gluing seam and were separated between the thumb and the middle finger by pulling off the topmost wafer. However, the mass production process which in the meantime is performed in connection with the production of photovoltaic cells requires an automatic process. Added to this is that the wafer formats continue to become larger.
At present, a wafer size of 156×156 cm has been reached, and the trend is toward 210×210 cm. At that time at the latest, for ergonomical reasons it will no longer be possible to manually separate the wafers.
In connection with an arrangement of the type mentioned at the outset and known from DE 199 04 834, the wafer stack is maintained on a support arm of a lifting device and dipped into a liquid, wherein the individual silicon wafers, still glued to a glass support plate, are horizontally arranged. The respectively uppermost wafer is separated from the glass plate with the aid of a tool and is conveyed to a cassette by means of a flow of liquid used as the conveying medium. The required cut-off of each individual silicon wafer requires time and holds the danger of damage to the edge of the respective silicon wafer. Moreover, grasping the separated silicon wafer out of the flow of liquid contains problems, because the individual silicon wafers can flip from their horizontal position out of the adhesive connection with the glass support plate, so that their exterior edge can adhere on the following lower silicon wafer. This problem becomes all the more serious, the larger the format of the silicon wafers is.